Young, low-mass brown dwarfs with mid-infrared excesses

We have combined new I, J, H, and K-s imaging of portions of the Chamaeleon II, Lupus I, and Ophiuchus star-forming clouds with 3.6 - 24 mu m imaging from the Spitzer legacy program "From Molecular Cores to Planet-Forming Disks'' to identify a sample of 19 young stars, brown dwarfs, and sub - brown dwarfs showing mid-infrared excess emission. The resulting sample includes sources with luminosities of 0.5 > log (L*/L-.) > - 3.1. Six of the more luminous sources in our sample have been previously identified by other surveys for young stars and brown dwarfs. Five of the sources in our sample have nominal masses that are at or below the deuterium-burning limit (12M(J)). Over three decades in luminosity, our sources have an approximately constant ratio of excess to stellar luminosity. We compare our observed spectral energy distributions (SEDs) to theoretical models of a central source with a passive irradiated circumstellar disk and test the effects of disk inclination, disk flaring, and the size of the inner disk hole on the strength / shape of the excess. The observed SEDs of all but one of our sources are well fitted by models of flared and/or flat disks.